Registration system for phasing simultaneously advancing webs of material having variable pitch lengths

ABSTRACT

Disclosed is a registration system and a method useful for controlling and correcting the phase and position of simultaneously advancing webs having pre-printed objects spaced at a pitch length characterized by small but significant pitch variation to a target web. Also disclosed are consumer products, such as disposable absorbent articles including the preprinted objects which were previously included in the webs phased before combining with a target web by utilizing the instant registration system. The pre-printed objects may include pre-printed, pre-bonded, pre-applied, pre-cut, or pre-glued objects or elements of disposable absorbent articles or registration marks produced on a separate independent process not control-linked to the instant registration method. The registration marks may be visible or normally invisible to the human eye.

[0001] This application is a Divisional application of the parentapplication U.S. Ser. No. 09/495,651 filed Feb. 1, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to a registration system and to amethod for phasing simultaneously advancing webs of materials, carryingpre-fabricated elements consecutively spaced at pitch lengths havingsmall but significant variation, to a target web. Further, the presentinvention relates to consumer products, such as disposable absorbentarticles, that may include an element or a registration mark which wasincluded in the continuous webs before phasing with the target web inthe process of making disposable absorbent articles by utilizing theinstant registration system.

BACKGROUND OF THE INVENTION

[0003] In the manufacture of disposable absorbent articles such asdiapers and catamenials, it is a common manufacturing practice tocombine continuously moving webs. These webs are typically representedby plastic films, non-wovens, elastics, etc. supplied to a convertingline in their original production form and do not require specialpositioning before combining with other materials. However, themanufacture of disposable absorbent articles may benefit if the abovematerials are supplied to the converting line as prefabricatedmaterials, i.e., produced off the converting line and carrying variouselements of disposable absorbent articles consecutively spaced along theweb length at a nominal pitch length determined by the length of aparticular absorbent article. Because the pitch length between theconsecutively spaced elements of the prefabricated materials can vary atsmall but significant variations, in order to ensure consistentpositioning of the product elements in every absorbent article, there isa demand for a method to phase or register the consecutively spacedprefabricated elements to desired positions on a target web beforecombining the prefabricated materials with the target web into a finalarticle or product.

[0004] The pre-fabricated elements may include preprinted registeredgraphic designs or characters that are desirably used in connection withdisposable articles such as diapers to enhance their outward appearancefor greater consumer acceptance. The positioning of a web preprintedwith registered graphics such that the graphics are properly placed inrelation to the rest of the diaper product is desirable, e.g., in orderto provide a large-sized graphic without cutting it at an incorrectlocation, has been typically problematic. This is important not only fordesirable aesthetic appearance, but also for example, because youngchildren may become disturbed at seeing graphic representations ofanimals cut up into pieces (e.g., a head cut off).

[0005] In addition, breathable polymer films that are particularlyuseful as backsheet materials for disposable absorbent articlestypically have good surface characteristics that make them suitable forthe application of multi-colored, high resolution graphics, but suchfilms tend to be mechanically unstable with a particular tendency towardthermal shrinkage in the machine direction. Such instabilitiescontribute to the difficulty in correctly positioning the pre-printedpolymer web on the product web such that the graphic is correctlypositioned, or phased, to the product web.

[0006] Various methods and apparatus have previously been used forcombining such components in a desired relationship. For example, inconventional “discrete phasing” operations, the product is built aroundthe printed graphic, by adjusting the timing position of the machineryin response to a correction signal. However, it cannot be used inoperations where more than one web bearing a preprinted (or other phasedobject) is required for the process, since the machinery can move inresponse to the graphics on one web only. See, e.g., InternationalPublication No. WO 96/29966.

[0007] In “non-continuous web placement” operations, the graphic-printedweb is discretized, or cut, into segments. Each segment is then placedon the target web or product in the desired position. This does not,however, ensure the centering of the graphic on the target web;furthermore, it limits the overall product design. The length of thediscretized segments must be less than the length of the product, whichmay allow leakage in the areas where the product is longer than thediscretized segment, for example, in the waist region of a diaper.

[0008] Other control systems and apparatus for registration have beendescribed, see International Publications WO 97/24094 and WO 97/24283.However, none of the existing systems or apparatus for registrationaddresses a system in which inherent significant material instabilitiesexist, nor do they address a system in which the pitch length of thepreprinted graphic is non-uniform, particularly if the preprinted pitchlength is longer than the pitch length of the product under production.Similarly, a control system such as that disclosed in U.S. Pat. No.5,766,389 requires a fixed target pitch. In practice, the target pitchcan be subject to the same instabilities as that of the registeredprinting.

[0009] Based on the foregoing, there is a need for a registration systemfor phasing simultaneously advancing webs having variable pitch lengths,at least one of which has consecutively spaced prefabricated objects(e.g., registered graphics), and the other of which (e.g., a diaperproduct web) contains consecutively spaced target objects (e.g.,absorbent cores). Furthermore, there is a need for a registrationcontrol system that can account for the material specific instabilitiesthat inherently exist in such webs and that present small butsignificant variations resulting therefrom, which make it difficult tocombine such webs. In addition, there is a need for a system in whichregistration of incoming webs having either longer or shorter pitchlengths than the pitch length of the product under production ispossible. None of the existing systems provides all of the advantagesand benefits of the present invention.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a registration system forphasing simultaneously advancing webs of material having variable pitchlengths comprising: (a) means for feeding a continuous target webcontaining consecutively spaced target objects along a path at a firstvelocity, the target web having a target web pitch length betweenconsecutive target objects; (b) means for feeding a continuouscontrolled web of material preprinted with consecutively spacedpreprinted objects along a path at a second velocity, the preprinted webhaving a controlled web pitch length between consecutive preprintedobjects; (c) detection means for detecting the preprinted objects of thecontrolled web by sensing by an optic that electronically strobes aresolver providing actual position data; (d) means for generating anerror signal based upon the detection of the preprinted objects of thecontrolled web and comparing to affixed target position constant; (e)means for adjusting the controlled web pitch length such that thecontrolled web pitch length is approximately equal to the target webpitch length to maintain registration due to pitch mismatch; and (f)means for adjusting the second velocity such that the preprinted objectsare shifted toward the target objects on the target web These and otherfeatures, aspects, and advantages of the invention will become evidentto those skilled in the art from a reading of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] While the specification concludes with claims particularlypointing out and distinctly claiming the invention, it is believed thatthe present invention will be better understood from the followingdescription which is taken in conjunction with the accompanyingdrawings, in which like designations are used to designate substantiallyidentical elements, and in which:

[0012]FIG. 1 is a plan view of a preferred embodiment of a disposablediaper of the present invention in a flat, uncontracted position showinga desired location for a preprinted graphic object;

[0013]FIG. 2A is a schematic diagram showing simplified representationsof a portion of a continuous diaper backsheet web having consecutivelyspaced graphics printed thereon and a portion of a diaper product web;

[0014]FIG. 2B is a top view of a diaper product web including arepresentation of the diaper core area;

[0015]FIG. 3 is a graphical representation of the pitch length variationtypically experienced by preprinted microporous materials that have beensubjected to typical conditions of winding and warehouse storage;

[0016]FIGS. 4A and 4B are perspective views of portions of preferredembodiments of laminates of microporous material and nonwoven material,illustrating the impact of running the microporous material at a pitchlength different from that of the nonwoven material;

[0017]FIG. 5 is a schematic diagram showing the process of combining twosimultaneously advancing webs;

[0018]FIG. 6 is a schematic diagram showing a preferred registrationcontrol system of the present invention;

[0019]FIG. 7 is a front view of a preferred embodiment of a disposableabsorbent article having registered graphics; and

[0020]FIG. 8 is a simplified plan view of another preferred embodimentof a disposable absorbent article having registered graphics.

DETAILED DESCRIPTION OF THE INVENTION

[0021] All references cited herein are incorporated herein by referencein their entireties. Citation of any reference is not an admissionregarding any determination as to its availability as prior art to theclaimed invention.

[0022] As used herein, the following terms are defined as follows.

[0023] “Machine direction” or “MD” means the direction of movement ofthe product along a manufacturing line. The machine direction is shownin FIGS. 1 and 5 as an arrow labeled MD.

[0024] “Phase” refers to the machine direction position of an objectexpressed as a degree of rotation. For example, the phase representationfrom 0° to 360° for a flat, uncontracted diaper 20 is shown in FIG. 1.The phase position of an object can be described as any identifiablefeature of the object. In FIG. 1, X° is representative of an exemplarydesired phase position of the graphic object 22.

[0025] “Product pitch length” means the length of material, on a relaxedbasis, that runs the full length of the product under production. Aproduct pitch for typical diaper products is illustrated as “PP” in FIG.2B.

[0026] “Registered process” means that two or more continuous webshaving phased features are combined in a correct phase relationship toone another.

[0027] “Registered graphics” refers to single or multiple color graphicobjects that are printed on a web close to a specified pitch length on arelaxed web basis. The registration system of the present inventionpermits small but significant variation from the intended product pitchlength of the product delivered.

[0028] “Target web” or “independent web” is the main web whichrepresents the product under production. This target web may be a diaperchassis with the leading edge of the absorbent core being a referencefor the target object. It is to be expected that this reference targetobject may also have a spacing with small but significant variations. Intypical use of the present invention an arbitrary once per product“strobe” is used as the reference. Small but significant variation instrobe locus relative to the passing of the reference target object isto be expected.

[0029] “Target object” means the location on the target web to which thepreprinted object on the controlled web is intended to align. Note thatalignment may take place at some standard offset from a easilyrecognizable feature or “target object.”

[0030] “Target web pitch length” means the nominal repeat length betweenconsecutively spaced target objects on the target web. The target webpitch length may contain small but significant variation during the useof the registration system of the present invention, e.g., ±2% betweenconsecutive target objects.

[0031] “Controlled web” or “manipulated web” means the preprinted webwhich is manipulated (extended or contracted) as needed to align thepreprinted object with the target object. Preferably, the controlled webis comprised of a microporous polymer film suitable for use as, or aspart of, a diaper backsheet.

[0032] “Preprinted object” means the prefabricated object produced offor on the converting line on a separate independent process notcontrol-linked to the registration process and located on the controlledweb at consecutively spaced, but typically not statisticallycontrollable, locations on the controlled web. The term “preprintedobject” as used herein may refer to preprinted, pre-bonded, pre-applied,pre-cut, pre-glued, and other objects or elements or a collection ofobjects (for example, graphics 122 in FIG. 8) of disposable absorbentarticles. Furthermore, the term “preprinted object” also refers toregistration marks to be used in the registration process; theregistration marks may be both visible and normally invisible to thehuman eye. The invisible mark cannot be differentiated by the human eyebetween the color of the preprinted object and the carrier web.

[0033] “Controlled web pitch length” means the repeat length betweenconsecutively spaced preprinted objects on the controlled web. Like thetarget web pitch length, the controlled web pitch length may containsmall but significant variation during the use of the registrationsystem of the present invention.

[0034] One embodiment of the present invention is directed to aregistration process for phasing simultaneously advancing continuoustarget and controlled webs, the target web containing target objects andthe controlled web containing preprinted objects, while permitting allin-running continuous webs to sustain small but significant variationsin the spacing of key objects (such as preprinted graphics). Suchvariations may result, for example, from virtual impossibility tomaintain a constant web tension during preprinting (due to machinevariations) and then in a roll form (due to inherent tensiondifferential among web layers of the roll), as well as climaticconditions affecting, for example, mechanically unstable microporouspolymer films during storage.

[0035] It is noted that any other polymer films, non-woven or wovenwebs, etc. capable of stretching under a tension force applied along theweb path, can be useful as controlled webs herein. It is also noted thatalthough the description of embodiments contained herein is primarilygiven in the context of a diaper converting line, i.e., registration ofpreprinted objects phased to diaper cores (target objects) on a diaperconverting line, it will be understood by those of skill in the art thatthe registration process herein may be used to phase multiplesimultaneously fed webs in any application.

[0036] In conventional unit operation registration processes, theposition of only a single phased web must be considered. The phase ofthe unit operation is advanced or retarded as needed to place thefunction of the unit operation in correct phase relationship to thesingle phased web. Such a system cannot be used, however, to combine twoor more incoming webs in correct phase, as the preprinted pitch lengthsof the target and preprinted objects on each will rarely be identical.

[0037] Where two or more webs each carrying phased objects must becombined in a predetermined relationship, information pertaining to thephase position of the target web, usually the product under production,e.g., the diaper chassis assembly, must be fed to the web handlingprocess. In addition, the position of the phased objects (e.g., apreprinted object, such as a preprinted graphic or a registration markon a polymer backsheet web or a non-woven topsheet) on each incoming,controlled web which is to be combined with the target web must also beknown and fed. As previously noted, the target web pitch length and thecontrolled web pitch length are rarely identical. It will be understoodby those of skill in the art that any incoming fed web may be designatedas a target web or a controlled web, and processed accordingly.

[0038] The continuous registration system of the present inventionperforms two functions simultaneously in order to correctly combine twoor more incoming webs having different phase positions, as describedabove. First, it continuously corrects the preprinted pitch length, orspacing of the graphics consecutively preprinted on the controlled web,to match the pitch length of the target web. Second, it continuouslysynchronizes the phase positions of the two webs such that they arecombined in the proper position, e.g., such that the graphic 22 iscorrectly located as desired on the diaper 20, for example, insubstantially the positions shown in FIGS. 1, 7 or 8.

[0039] In one embodiment, the target web comprises that part of thediaper chassis itself that is generally continuously comprised of thecore and topsheet assembly, prior to the attachment of the backsheetweb. The target web is represented in FIGS. 2A and 2B as target web 40.The target web 40 contains target objects 42 consecutively but notequidistantly spaced thereupon at a target web pitch length, “Ltp”.Target objects 42 may be the absorbent cores of the disposable diaperchassis. Ltp need not be identical to the product pitch length PP of thediaper product; in fact, the target web 40 will likely have small butsignificant variation in consecutive product pitch lengths PP due toclimatic conditions during storage and transport, thermally inducedcreep, and the like. In addition, it is noted that the pitch length Lppof the controlled web 30 may be either longer or shorter than Ltp.

[0040] It is noted that the target object position may be directlysensed or inferred from the use of an electronic strobe. One embodimentof the present invention uses an electronic strobe. This signal happensonce per machine cycle at the same place in the machine cycle. Forexample, if the machine cycle is represented by 1000 counts, then thestrobe may be arbitrarily set at 500 to 600 “on” and balance of cycle“off”. The leading edge transition between “off” to “on” marks a machinetime fixed position to which a graphic is registered. When the system isfirst started up, the operator inputs an offset value using an“advance/retard” button while examining the position of the controlledweb graphic using an actual strobe light. Once the offset value is set,the registration system will target the controlled web graphic to thesame point in the machine cycle.

[0041] Again referring to FIG. 2A, the controlled web 30 may comprise acontinuous film material, for example, a breathable microporous polymerfilm, that is used as part of the diaper backsheet. The controlled web30 has preprinted objects 22, consecutively but not equidistantlyprinted thereupon at a particular controlled web pitch length, “Lpp”.Lpp is invariably something other (either longer or shorter) than boththe product pitch length PP and the pitch length of the target web Ltpdue to climatic conditions, thermally induced creep, and the like. Anexemplary Lpp is shown in FIG. 2A. Preprinted objects 22 may beregistered graphics that are colorful, high resolution designs that areappealing to the consumer, who is typically a care-giver to the wearerof the diaper, or who in other cases may actually be the wearer.

[0042] As noted above, in most cases, Ltp is not equal to Lpp; in fact,exact matches are highly improbable. This difference is a major sourceof the difficulties associated with proper phasing of the controlled web30 and the target web 40. As can be most clearly seen in FIG. 2A, apitch delta C (e.g., Ltp minus Lpp) usually exists and must be correctedin order to insure proper product phasing. It is additionally noted thatthe pitch delta C associated with Ltp and Lpp typically accumulates foreach subsequent target object 42, and thus a greater amount ofcorrection is generally needed. This error accumulation of pitch deltais represented in FIG. 2A as C, C2, C3, C4.

[0043] The corrections of pitch delta C, C2, etc. associated with theregistration system of the present invention may not actually benecessary for product functionality; however, they are criticallyimportant for consumer acceptance of the diaper products produced. And,in some cases, children wearing a disposable article herein that has animproperly phased graphic, e.g., an animal with its head cut off, may beupset.

[0044]FIG. 3 illustrates the instabilities in controlled web pitchlength Lpp that may arise due to the inherent thermal instability of themicroporous polymer films of the present invention. Such thermalinstability leads to differential shrinkage of the microporous film, andsignificant variations in Lpp frequently result. Referring to FIG. 3,the position along a wound roll (i.e., a continuous, controlled web 30)of microporous polymer film that has been preprinted with registeredgraphics is represented on the X axis. The start of the roll isindicated at the origin of the axes, while moving to the right along theX axis indicates moving toward the core of the roll, corresponding tounwinding the roll.

[0045] On the Y axis, preprinted pitch length Lpp is represented inmillimeters. As can be seen, differences in preprinted pitch lengths Lppof up to about 10 mm may be seen between various locations on the sameweb of material.

[0046] The registration system of the present invention is thus designedto overcome the phasing problems associated with combining the targetweb 40 and the controlled web 30 where Ltp is not equal to Lpp, whereLpp is inherently variable, and where both webs are simultaneously andcontinuously fed to a combining operation. The process has the abilityto on-goingly adjust the pitch length of the controlled web 30 asdelivered to match or to more closely approximate that of the target web40. In addition, the system of the present invention makes suchcorrection in a gentle, non-abrupt and gradual fashion so as to accountfor the delicate nature of the web, which may be a microporous polymerfilm, without damaging it. Alternatively, if conventional higherstrength webs are used, the system is capable of making more rapid andabrupt adjustments that. may not be acceptable with the microporouspolymer films.

[0047] As described more fully below, this is accomplished by the use ofweb tension transients to change the preprinted pitch length Lpp of thepreprinted objects on the controlled web 30. Changing the tension in aweb causes a change in the pitch length of the web. Thus, more tensionstretches the material of controlled web 30, causing the pitch lengthLpp to increase, while less tension relaxes the controlled web 30,causing the pitch length Lpp to decrease. The absolute tension in thecontrolled web 30 should not approach zero tension, as control of thecontrolled web 30 would be lost. Conversely, more or less web may bemetered to the process, which also changes the level of tension in theweb.

[0048] The system of the present invention thus introduces small tensiontransients, which provides on-going correction. This serves to maintainthe integrity of the delicate, mechanically unstable polymer films thatare useful for disposable absorbent articles herein. It also serves tocorrect the phase relationships of objects on the each incoming web inincrements that are too small to be detected by the web handlingprocess, which means that there is little possibility for the amount oferror to become large enough to trigger the shut-down functions of theweb handling process. In addition, it allows for manufacture ofconsecutive products that may have insignificant differences in thelocations of the graphic objects on each product.

[0049] Any control algorithm that creates such small on-going transientsis useful herein. The control system prepares small transientcorrections in a timely fashion that intervene in the control ofincoming web handling drives to prevent mismatches between the positionsof the target object and the preprinted object from drifting out of thezone that the consumer would find acceptable. Exemplary controlalgorithms herein include manual control, a control algorithm based onstatistical process control, or a PID control system.

[0050] It is believed that control systems relying on statisticalanalysis of past history such as running average are simply too sluggishto stay ahead of the significant variation observed in the position ofgraphics on the in-running controlled web 30. To avoid the complexity ofcontrolling multiple drives to position the graphic, a preferredembodiment herein is a PID control algorithm which controls the feedrate of the controlled web 30 only as necessary to minimize the strobeddistance between a fixed position of converter machine time withuser-set offset and the sensed mark. If the space between the sensedmarks of the controlled web 30 (Lpp), is longer than the target pitchlength Ltp, more web 30 is fed to the process, reducing the web tensionand allowing the space between graphics to contract. Conversely, if thespace between the sensed marks of the controlled web 30 is too short,less web is fed, causing an increase in web tension causing the spacebetween marks to increase. In this way, not only is the pitch of the webbrought close to the pitch of the product, but the position of thegraphic is brought close to the target position.

[0051] To determine the position of the preprinted objects on controlledwebs various detectors/scanners may be used. For example, to determinethe position of the color graphic on the incoming controlled web 30, asensor is selected which detects differences between light passingthrough the web via different printed colors. The color of the targetweb object, the position of the target web object relative to otherobjects of the same color, and the size of the target object combine tocreate the means for generating a clean signal whose position is strobedonce per machine cycle.

[0052] Alternative means of establishing position of preprinted objectsinclude: 1) sensing a visible timing mark on a part of the web that islater removed by the process; 2) sensing a normally invisible to thehuman eye registration mark which may or may not remain a part of afinal article or product; or 3) using a grid of sensors to look for arecognized pattern of light diffusion.

[0053] The invisible preprinted objects may be detected, for example, ifthey can fluoresce. Fluorescence is the process whereby light isabsorbed by a substance, called a fluorophore, at one wave length andthen re-emitted at a longer wave length. It should be noted that anyelectromagnetic waves of any length may be used for detecting thewave-emitting preprinted objects, however, a preferred wave lengthspectrum for detecting invisible marks on disposable absorbent articlesis the infrared (IR) region of the electromagnetic spectrum includingwave lengths from about 700 nm to about 2,500 nm, and a more preferredwave length spectrum is the near infrared (NIR) region including wavelengths generally from about 700 nm to about 1,100 nm. Another invisiblewave length spectrum which may be used for detecting invisible marks isthe ultraviolet (UV) region including wave lengths from about 1 nm toabout 400 nm. (The visible region of the electromagnetic spectrum islocated between the IR and UV regions and includes wave lengths fromabout 400 nm to about 700 nm.) The NIR mark is preferred over the UVmark in some instances because the UV mark may fluoresce or “glow indark” under certain conditions of home lighting because it may fluorescelonger than UV waves and thereby becomes visible to consumers. The NIRmarks may include inks containing substances that fluoresce primarily inthe NIR region of the electromagnetic spectrum, as, for example, are theinks described in U.S. Pat. No. 4,540,595 entitled “ArticleIdentification Material and Method and Apparatus For Using It,” issuedto Acitelli et al. on Sep. 10, 1985 and U.S. Pat. No. 5,665,151 entitled“Method For Making Articles With And Detecting Water Based InksContaining Near Infrared Fluorophores,” issued to Escano et al. on Sep.9, 1997, each of the patents is incorporated herein by reference. TheNIR marks may be detected, for example, by using Smarteye® STEALTHsensor made by TRI-TRONICS® Co., Inc. of Tampa, Fla.

[0054] The PID control system shown in FIG. 6 seeks to minimize theerror distance which is observed once per product. The proportional gain(Kp) 71 sends a correction signal to the controlled web feed drive thatis proportional to the size of the error. The integral gain factor (Ki)74 is set to eliminate the steady state offset typical of purelyproportional control. While a differential gain factor may also be used,it is believed that best results are obtained by setting this equal tozero. It is observed in FIG. 6 that the error signal trims the operationof the feed drive which is typically running at “gear ratio” relative torate of product production. Although speed and position may vary, onaverage one preprinted object must be processed per target product.

[0055] The registration system of the present invention preferablyadjusts the pitch Lpp of the controlled web 30 by on-goingly adjustingthe tension in the controlled web 30. The Lpp is adjusted to “Lc”, whichis used herein to mean “length at combining.” Lc is equal orapproximately equal to Ltp, i.e., the pitch length of the controlled web30 is made approximately equal to that of the target web 40 so that thepreprinted object, for example, graphic 22, can be positioned in thecorrect phase relationship to the product. This tension acts through theweb modulus, Ew, of the controlled web 30, according to the followingequation:

Lc=(1+ε)×Lpp=(1+T/Ew)×Lpp, where

[0056] ε=strain;

[0057] T=controlled web tension; and

[0058] Ew=web modulus of controlled web.

[0059] The foregoing equation acts for all webs being combined together.Thus in the case of two webs:

Lc1=(1+T1/Ew1)×Lpp1 and Lc2=(1+T2/Ew2)×Lpp2.

[0060] As noted above, at the point of registered combining under steadystate conditions, Ltp is equal to Lc. Thus, the ratio of the relaxedlengths combined at any time is given by the equation:

Lc1/Lc2=(1+T2/Ew2)/(1+T1/Ew1).

[0061] The tension variables T as well as the modulus variables Ew eachhave a range of variation, so the ratio of the Lc values will alwaysvary somewhat from unity. The difference between the Lc ratio and unityis referred to herein as “puckering”:

Puckering %=(Lc1/Lc2−1)×100.

[0062] The puckering value can assume positive or negative valuesdepending which web has the least relaxed length. After the finishedproduct is cut apart, the combined web is pulled to the length of theincoming web with the least relaxed length. This causes the other web to“pucker.” Above a certain tolerance level, puckering has a noticeableimpact on the appearance of the product. For a diaper backsheet formedfrom a nonwoven material and a polymer film preprinted with graphicdesigns, puckering levels up to about ±2%, while noticeable, aregenerally not perceived as distorting the appearance of the product.

[0063] Alternatively, different puckering levels can intentionally becreated, or puckering may otherwise be controlled to create materialswith different tactile feels as desired. Note that even below ±2% thatpuckering can be controlled and located on the product according to thepresent invention to minimize its impact on product appearance. To dothis, the laminated material furthest away from the consumer is overfedand pulled back, thus hiding the puckering from the consumer.

[0064] The present invention has the capability of registeringcontrolled webs having pitch lengths that are not uniform, and which canbe either longer or shorter than the machine product pitch length. Theability to register materials with pitch lengths longer than the productunder production allows the designer of such a product to tailor thesurface texture of the product. This is demonstrated in FIGS. 4A and 4B,where two materials are laminated together by passing through a nippoint. The material which is longer than the finished product pitch ispulled back by the other material. By making the layer of the laminatethat is furthest away from the eye of the consumer the material that ispulled back, the impact of the registration process on the texture ofthe finished product is mitigated.

[0065] In FIG. 4A, the pitch length of the nonwoven web 32 (Ltp) whichmay form a portion of the diaper backsheet is longer than the pitchlength (Lpp) of the polymer film (controlled web) 30. In this case,after the final cut that separates the consecutive diaper products, thepolymer film pulls back the nonwoven material. This creates a roughenedtexture on the exposed surface of the laminate which the consumer cansee and feel.

[0066]FIG. 4B shows the surface texture impact of the pitch lengths(Lpp) of the polymer film (controlled web) 30 longer than the pitchlength (Ltp) of the nonwoven material web 32. In this case, the nonwovenmaterial pulls back the polymer film material after the final cut. Thus,the impact of the unequal combining is manifested on the inside of theproduct and is hidden from the eye of the consumer. Thus, it isgenerally preferable to overfeed the controlled web of polymer filmmaterial so that the consumer does not see or feel the roughenedtexture.

[0067] The nonwoven material 32 may be fed into the system as anindependent web having phased objects with variable pitch length. Insuch a case, the nonwoven web and preferably the controlled web arephased as described herein, and combined; then the combination laminatematerial is phased and combined to the target web (diaper product web)as described herein.

[0068] Assuming that a puckering tolerance level of up to about ±2% isacceptable, the available adjustment rate for registered graphics islimited. It is important to design the registered printing such that areasonable tolerance of graphic position is accommodated. The graphicposition tolerance should be greater than or equal to the web to webposition shift typically seen at the time of web splicing; that is, atthe time that a subsequent roll of preprinted web is supplied to the webcombining process at the time that the previous roll is used up by theprocess. The roll to roll error is different and generally greater thatthe normal variation within a single roll. Thus, if random splicing wereused, phasing corrections of up to 180 degrees (half of a full length)would sometimes be necessary. During such times, all product producedwould need to be scrapped. The splice tolerances of the presentinvention are controlled in concert with the tolerances of preprintedobject position to reduce splice time rejected product to ideally zero(other than rejection of the splice tape itself).

[0069] The selection of the raw material to be used for the backsheet,i.e., the controlled web 30, may be constrained by both the productdesign and the registration system of the present invention. The keyparameters that may be unique to registered graphics are impacted by theneeds of product functionality. For diaper backsheet, a preferredmaterial is a breathable microporous polymer film. A preferredmicroporous polymer film is formed from a mixture of polyethylene andcalcium carbonate, and titanium dioxide if needed to increase the whiteappearance of the film, since whiteness is a film characteristic that isnecessary for widespread consumer acceptance. More preferably, themicroporous polymer film has high thermal stability characteristics inorder to support the printing of high resolution color graphics thereon.Preferably the film meets a maximum of ±1% repeat pitch variation, i.e.,mismatch, but more typically ±2% is likely to be seen. It is believedthat puckering ratios ranging from about 0.97 to about 1.015 maysuccessfully be provided using this system, making it possible to handlefilms with an even wider range of pre-printed pitch length variation.

[0070] Other preferred characteristics of the microporous polymer filmthat are important in assuring good processing with the registrationsystem of the present invention include: web modulus (preferably fromabout 4000 to about 13,000); coefficient of friction (preferably highenough so that the system metering nips can act on the web with asustainable level of web tension); and thermal enthalpy (preferably highenough to have sufficient heat resistance during hot melt gluelamination, but not increased to the point that the stiffness of thefilm increases to the point of discomfort for the wearer).

[0071] The process of combining the two webs 30 and 40 is schematicallyrepresented in FIG. 5. The controlled web 30 is initially fed at avelocity Vo. The target web 40 is fed to the combining stage 50 at avelocity Vt. Detection of the position of a preprinted object (e.g.,graphic 22) of the control web 30 moving in the machine direction MDoccurs at preprinted object detection stage 33 via an optic 34 whichelectronically strobes a resolver 50 a providing actual position data 50b of the preprinted object 22 (see FIG. 6). Similarly, detection of atarget object (e.g., diaper core 42) on the target web 40 moving also inthe machine direction MD, occurs at the product detection stage 45,preferably manually by an operator setting the target position constant44 (see FIG. 6) which is the target position of the preprinted object 22for combining the preprinted object (graphic 22) with the correspondingtarget object (core 42), or alternatively, via any suitable opticworking in combination with resolver 50 a sensing the target object 22on the target web 40 (i.e., automatically).

[0072] As previously noted, the process control dilemma that theregistration system of the present invention must correct is two-fold.

[0073] First, pitch mismatch must be corrected. There is a difference inpitch between the online made web (target web 40) and the offline madeweb (control web 30). This difference in pitch is shown in FIGS. 2a and5, as the difference between Ltp and Lpp, where Ltp−Lpp =pitch delta C).As described in connection with FIG. 2a, this pitch 17. delta Caccumulates as the number of products accumulates. Thus, for the firstproduct, the pitch delta is about C; for the second product, the pitchdelta is about C2; for the third product, the pitch delta is about C3,and so on.

[0074] Second, phase correction is needed. Phase error may be causedwhen a transient change occurs in the controlled web 30 via a controlweb splice or some phase upset in the position of the preprinted object22 in relationship to the target object 42.

[0075] In a preferred PID control system of the present invention, errorsignal 70, see FIG. 6, is generated based upon recording of position ofincoming timing mark by resolver strobe. This error signal istransformed into a correction signal via a PID algorithm. In a preferredalgorithm, integral gain is used to attenuate steady state error, anddifferential gain is preferably set at zero. This correction signalforces a programmable drive or differential correction shaft to speed upor slow down the axis driving the controlled web 30 at a metering point30 b. Thus, Vo is adjusted to Vc (see FIG. 5) by gain factors 71 and 74,see FIG. 6, to maintain the position of the preprinted object graphic 22and the target object core 42, by changing flow rate of the controlledweb 30.

[0076] Referring to FIG. 6, a preferred registration control system 60is shown. The main reference signal is provided by the resolver 50 a andis referred to as the converter position reference signal 62. Theconverter position reference signal 62 is the resolver change inposition over time, i.e., a velocity reference signal (preferably onerevolution of the resolver per target object 42). This signal 62 isequal to the pitch length of the product times the converter rate. Theregistration control system 60 provides a trim correction factor, whichis typically a small percentage of the servo velocity reference signal76, to the converter position reference signal 62, based on the pitchmismatch and phase correction described above, by automaticallycalculating an error signal 70 and adjusting the servo system velocityvia the velocity loop 78, to change the flow rate of the control web 30.This is accomplished by the controlled web 30 preprinted object 22 beingsensed by optic 34 that electronically strobes resolver 50 a providingactual position data 50 b (feedback), and comparing it to the fixedtarget position constant 44. This error signal 70 is manipulated tomaintain registration due to pitch mismatch and phase correction.

[0077] The pitch mismatch aspect of the control dilemma is used to limitthe accumulating offset, i.e., pitch delta C, C2, C3, and so on.Integral gain Ki (auto correction 74) is multiplied by the basereference signal 75 to yield a servo velocity signal 76 to the velocityloop of the servo drive 78, thus matching the pitch of the controlledweb 30 to the target web 40. The proportional gain Kp 71 is needed tostabilize the system and provide enough gain to maintain the targetposition 44.

[0078] The phase correction aspect of the control dilemma, i.e., theprocess control issue, is used to phase the system for several reasons.First, initial set-up of the registration system 60 online requiresphase correction. When the registration system 60 is first started up,the position of the preprinted object 22 assumes an arbitrary butcontrolled position relative to that of the target object 42. Thisarbitrary position may be out of phase, requiring the operator to changethe fixed target position constant 44 to initially set the preprintedobject 22 to the target object 42 (from this time on no additionalmanual intervention is needed). Proportional gain 71 is needed to drivethe system 60 to new setpoint, target constant 44. The error signal 70is multiplied by a proportional gain factor 71 and then added to aconverter position reference 50 a to generate a base reference signal75.

[0079] In addition, web splicing of control web 30 causes a phase error,requiring phase correction. Proportional gain 71 is needed to drive thesystem to the set point target constant 44.

[0080] Previous design efforts targeting registered graphics have beenbased upon separate control systems for incoming graphics pitch lengthcorrection and phase position control. However, the system of thepresent invention incorporates simultaneous correction based upon therelationship between pitch length and the velocity. It will beunderstood by those of skill in the art that position has an integralrelationship to velocity and can therefore be controlled using the samesystem that controls velocity.

[0081] Disposable diaper products typically include a topsheet material,an absorbent core, and a backsheet material. The topsheet material islocated to be placed facing the body or nearest the body when the diaperis worn and is generally provided with a liquid permeable region so thatbody exudates can flow through the topsheet to the absorbent core, wherethey are contained. The backsheet material, which is placed away fromthe body during wear, is typically liquid impermeable so that outerclothing or other articles such as bedsheets are not wetted by the bodyexudates. Such an exemplary diaper is disclosed in, for example, BuellU.S. Pat. No. 5,569,234, directed to a “Disposable Pull-on Pant”.

[0082] In addition to the basic topsheet, core, and backsheetcomponents, it will be understood by those of skill in the art that manyother features for disposable absorbent articles are within the scope ofthe present invention. For example, barrier cuffs as described in Lawsonand Dragoo U.S. Pat. Nos. 4,695,278 and 4,795,454 are a desirablefeature for disposable absorbent articles. In addition, skin care typetopsheets that are provided with lotion thereon for the purpose ofreducing skin irritation and chafing are a desirable feature herein.

[0083] Referring to FIG. 7, there is shown an exemplary disposablepull-on diaper 150, which is generally pulled onto the body of thewearer by inserting the legs into the leg openings 162 and pulling thearticle up over the waist. Generally, “pull-on diaper” refers to pull-ongarments worn by small children and other incontinent individuals toabsorb and contain body exudates. It should be understood that otherpull-on garments such as training pants, incontinent briefs, femininebriefs, feminine hygiene garments or panties, and like, are includedherein.

[0084] Referring to FIGS. 7 and 8, the diaper 150 is generally comprisedof a backsheet 152, a topsheet 154 and an absorbent layer 156 (shown indashed lines in FIG. 8) located between the backsheet 152 and thetopsheet 154. The backsheet 154 is the surface which faces away from thewearer's body, while the topsheet 152 is the surface which faces towardthe wearer's body. In one embodiment of the present invention, thebacksheet 152 is comprised of at least a microporous polymer filmprinted with registered graphics, e.g., 120, 122, as described herein.The backsheet 152 may further comprise a layer of nonwoven material (seereference numeral 32, FIGS. 4A, B) laminated or otherwise secured to themicroporous film layer, in which case there is provided a morecloth-like and garment-like feel. In such a case, the nonwoven web maybe fed to the web handling process as a continuous incoming web and maybe combined in a desired relationship with the controlled web 30 and thetarget web 40.

[0085] In the case of a laminated nonwoven backsheet, it is desirablethat the surface texture of the non-woven not be impacted by a laminatedsublayer, e.g. a microporous polymer film sublayer, which pulls it backand causes it to “pucker.” It is more desirable that any puckering thatis required for the operation of a registration system be limited to theunderlying polymer material, which is neither seen nor felt by the userof the product, see FIG. 4B. The system of the present invention can beused in cases where the pitch length Lpp of the microporous film web(controlled web 30) may be longer or shorter than that of the product,Ltp. Overfeeding the target web may lead to superior surface texture.After the final cut, when Lpp is less than Ltp, the film material pullsback the nonwoven material that forms part of the product. This createsa roughened texture of the exposed surface of the laminates where theconsumer can see and feel. This, when Lpp is greater than Ltp, theimpact of the unequal combining upon which the registration systemsdepends is hidden from the consumer. In general, Lc should be greaterthan both Lpp and Ltp, to avoid the possibility of a zero-tensionsituation.

[0086] Elastically extensible side panels 156 are provided to ensuremore comfortable and contouring fit by initially conformably fitting thepull-on diaper 150 to the wearer and sustaining this fit throughout thetime of wear well past when it has been loaded with exudates. Legelastics 158 and waist elastic region 160 are also provided to enhancethe fit around the legs and waist, respectively.

[0087]FIG. 7 shows the front view of the diaper 150 with an exemplarygraphic 120 positioned in about the upper region of the backsheet, onthe front side of the diaper 150. In FIG. 8, there is shown a simplifiedplan view of an embodiment of a disposable absorbent article in itsflat, uncontracted state prior to formation. In this embodiment, graphic120 is shown in the back region of the diaper with graphics 122additionally shown in the front region of the diaper.

[0088] It is understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to one of skill in the artwithout departing from the scope of the present invention.

What is claimed is:
 1. A registration system for phasing simultaneouslyadvancing webs of material having variable pitch lengths, the systemcomprising: a. means for feeding a continuous target web containingconsecutively spaced target objects along a path at a first velocity,the target web having a target web pitch length between consecutivetarget objects; b. means for feeding a continuous controlled web ofmaterial preprinted with consecutively spaced preprinted objects along apath at a second velocity, the controlled web having a controlled webpitch length between consecutive preprinted objects; c. detection meansfor detecting the preprinted objects of the controlled web by sensing byan optic that electronically strobes a resolver providing actualposition data; d. means for generating an error signal based upon thedetection of the preprinted objects of the controlled web and comparingto a fixed target position constant; e. means for adjusting thecontrolled web pitch length such that the controlled web pitch length isapproximately equal to the target web pitch length to maintainregistration due to pitch mismatch; and f. means for adjusting thesecond velocity such that the preprinted objects are shifted toward thetarget objects on the target web.
 2. The registration system of claim 1further comprising means for combining the target web and the controlledweb such that the target objects and the preprinted objects are phased.3. The registration control system of claim 2 wherein the target web iscomprised of diaper chassis and the controlled web is comprised of amicroporous polymer film.
 4. The registration control system of claim 1wherein the means for adjusting the controlled web pitch length suchthat it is approximately equal to the target web pitch length compriseson-goingly adjusting the tension in the controlled web.
 5. Theregistration system of claim 1 wherein the controlled web pitch lengthis greater than the target web pitch length to pucker the controlled webto provide desired visual and tactile properties to a finished product.6. The registration system of claim 5 wherein the controlled web has apuckering level of up to +/−2%.
 7. The registration system of claim 1wherein the target web pitch length is greater than the control webpitch length to pucker the target web to provide desired visual andtactile properties to a finished product.
 8. The registration system ofclaim 5 wherein the target web has a puckering level of up to +/−2%. 9.The registration system of claim 1 wherein the controlled web pitchlength is greater than a product pitch.
 10. The registration system ofclaim 1 wherein the target web pitch length is greater than thecontrolled web pitch length.
 11. The registration system of claim 1wherein the controlled web pitch length between consecutive preprintedobjects is variable.
 12. The registration system of claim 1 wherein thepreprinted object includes an element of a disposable absorbent article.13. The registration system of claim 1 wherein the preprinted objectincludes a registration mark.
 14. The registration system of claim 1wherein the preprinted object is normally invisible to the human eye.15. The registration system of claim 1 wherein the preprinted objectincludes a fluorophore.
 16. The registration system of claim 11 whereinthe fluorophore is capable of emitting electromagnetic wavelengths inthe infrared (IR) spectrum from about 700 nm to about 2,500 nm.
 17. Theregistration system of claim 11 wherein the fluorophore is capable ofemitting electromagnetic wavelengths in the near infrared (NIR) spectrumfrom about 700 nm to about 1,100 nm.
 18. The registration system ofclaim 1 wherein the preprinted object includes a registered graphic.